He's talking about the inability to specify an interface that specifies functions that take two arguments of the same type. Go can't do that.
You can sometimes work around it. For instance consider sorting. The natural approach is to specify a type that allows comparisons. Go can't do that. But in go you can have a collection which has a function Less(i, j int) bool that takes in two integers and compares the objects at those positions (which in turn just happen to be of the same type).
But this is a limited work around, and there are plenty of cases where you can want something more flexible.
You can sometimes work around it. For instance consider sorting. The natural approach is to specify a type that allows comparisons. Go can't do that. But in go you can have a collection which has a function Less(i, j int) bool that takes in two integers and compares the objects at those positions (which in turn just happen to be of the same type).
But this is a limited work around, and there are plenty of cases where you can want something more flexible.